1. Field of the Invention
A sensor system and method are provided having a digital signal processing unit adapted for providing sensitivity enhancement. Sensitivity enhancement is provided by attenuating white noise within a frequency band corresponding to a signal of interest utilizing the white noise that is distributed in a frequency spectrum outside the frequency band that corresponds to a signal of interest. In particular, the system and method make use of a matrix digital signal processor to convert a digital signal, the digital signal being representative of a signal output from a sensor, from a single event time domain signal with N time domain samples to N frequency domain samples, where N is an integer greater than 1. The N frequency domain samples represent a frequency spectrum at least N times greater than what is typically referred to as the “matched filter bandwidth” of the signal output from the sensor. The energy of a multi-event signal (i.e. multiple N sample inputs) is obtained by coupling the output of the matrix digital signal processor to a mode digital signal processor. The mode digital signal processor computes an average signal energy over an extended time period of multiple signal energy values output by the matrix digital signal processor.
2. Prior Art
The sensitivity of sensors, including radio frequency receivers, is defined as the ability to detect or perceive a given phenomenon, condition or level and one major limitation thereof is naturally occurring white noise. The power of this noise within the sensor or receiver reception bandwidth is given by the well-known formula:W=KTFBG; where, “W” is the nominal or average noise power, “K” is Boltzmann's Constant, “T” is the absolute temperature, “F” is the noise figure, “B” is the reception bandwidth and “G” is the gain.
Those knowledgeable in the art, including the inventor, consider single input event sensitivity enhancement attempts that use non-linear signal processing as being ineffective at enhancing sensitivity for most applications.
The prior art generally linearly optimizes the sensitivity of receivers and sensor systems by placing a preamplifier as early in the reception chain of circuit elements as practical and by using a preamplifier with a gain that is sufficiently large that the noise figure of subsequent circuits is effectively irrelevant. Further, a high quality preamplifier is used that has a small noise figure. The final conventional linear method of optimizing sensitivity is to match the reception bandwidth to the signal bandwidth in order provide an optimum signal to noise ratio (SNR). Another method of optimizing sensitivity, although in most cases somewhat impractical, is to cool (significantly) the preamplifier and other front-end hardware. This is usually accomplished with either a special refrigeration system or by immersion into a bath of liquid nitrogen.
It is has been widely believed that it was not possible to use linear signal processing to attenuate the white noise without simultaneously attenuating the signal. When the input consists of multiple time domain samples that are transformed to frequency domain samples or cells, and the width of what we designate as the designated cell is equal the bandwidth of the desired signal, practitioners of the prior art have assumed that the noise visible outside the designated cell is of no use in assessing the noise in the designated cell.
However, in contrast to the prior art, the inventor has been found that it is possible to linearly attenuate the noise in the designated cell without attenuating the desired signal. The noise values in the remaining frequency domain cells are determined and used to attenuate the noise component in the designated cell using a matrix digital processing system and method.